The invention relates to teat cup assemblies employing a silicone inflation or liner with an outer shell. Use of silicone inflations or liners rather than natural or synthetic rubber is known to be desirable. An article in New Zealand Journal of Dairy Science and Technology, 12.238-241, 1977, discusses the advantages of use of silicone as compared to teat cup liners made from synthetic or natural rubber. Basically the silicone inflations or liners do not absorb butter fat and oils or moisture as do the rubber liners. Additionally, silicone has resistance to extremes of temperature, ability to retain its flexibility even at low temperatures and good resistance to sunlight, oils, solvents and other chemicals. However, the silicone does have certain disadvantages and the commercial silicone teat cup liners suffer from these disadvantages. Silicone has a low tear resistance and is easily punctured. This problem is noted as the primary disadvantage of silicone liners in the above-cited New Zealand article. In the art silicone inflations have been developed to fit existing shells designed for rubber inflations and very little attention has been devoted to developing a shell adapted to protect the silicone inflation. In one prior art device made by BouMatic the distal end of the liner is exposed to impact and can be damaged by a variety of impacts for example, hitting the concrete floor, or the grates in the milking parlor, hitting other cups or equipment and even being stepped on by the cow. An impact on the distal end can cause a shearing action of the cap and shell to cause damage. Accordingly, the useful life afforded by the use of silicone which is normally significantly higher than that for a rubber inflation can be shortened considerably by an impact of this character which can split, tear or cause puncturing of the silicone inflation.
U.S. Pat. No. 4,459,938 discloses a teat cup assembly employing a two-piece silicone rubber inflation with an entrance member 20 and inflation 16. A multiple piece shell with a protective cap covers the distal end of the inflation. This patent shows a structure which is difficult to assemble and disassemble and results in hard to clean pockets which can collect dirt.
Other types of shell constructions such as those illustrated in U.S. Pat. Nos. 4,332,215; 4,116,165 and 3,659,557 show shells which afford some protection for the distal end of the liner but require a ring to expand the liner to secure the liner inplace in the shell and to provide a seal. The machine installation process to install the ring can tear the liner if a silicone liner is employed.